Patch "bridge: fix br_stp_set_bridge_priority race conditions" has been added to the 4.0-stable tree

Patch "bridge: fix br_stp_set_bridge_priority race conditions" has been added to the 4.0-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    bridge: fix br_stp_set_bridge_priority race conditions

to the 4.0-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     bridge-fix-br_stp_set_bridge_priority-race-conditions.patch
and it can be found in the queue-4.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Fri Jul  3 19:59:52 PDT 2015
From: Nikolay Aleksandrov <razor@blackwall.org>
Date: Mon, 15 Jun 2015 20:28:51 +0300
Subject: bridge: fix br_stp_set_bridge_priority race conditions

From: Nikolay Aleksandrov <razor@blackwall.org>

[ Upstream commit 2dab80a8b486f02222a69daca6859519e05781d9 ]

After the ->set() spinlocks were removed br_stp_set_bridge_priority
was left running without any protection when used via sysfs. It can
race with port add/del and could result in use-after-free cases and
corrupted lists. Tested by running port add/del in a loop with stp
enabled while setting priority in a loop, crashes are easily
reproducible.
The spinlocks around sysfs ->set() were removed in commit:
14f98f258f19 ("bridge: range check STP parameters")
There's also a race condition in the netlink priority support that is
fixed by this change, but it was introduced recently and the fixes tag
covers it, just in case it's needed the commit is:
af615762e972 ("bridge: add ageing_time, stp_state, priority over netlink")

Signed-off-by: Nikolay Aleksandrov <razor@blackwall.org>
Fixes: 14f98f258f19 ("bridge: range check STP parameters")
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/bridge/br_ioctl.c  |    2 --
 net/bridge/br_stp_if.c |    4 +++-
 2 files changed, 3 insertions(+), 3 deletions(-)

--- a/net/bridge/br_ioctl.c
+++ b/net/bridge/br_ioctl.c
@@ -247,9 +247,7 @@ static int old_dev_ioctl(struct net_devi
 		if (!ns_capable(dev_net(dev)->user_ns, CAP_NET_ADMIN))
 			return -EPERM;
 
-		spin_lock_bh(&br->lock);
 		br_stp_set_bridge_priority(br, args[1]);
-		spin_unlock_bh(&br->lock);
 		return 0;
 
 	case BRCTL_SET_PORT_PRIORITY:
--- a/net/bridge/br_stp_if.c
+++ b/net/bridge/br_stp_if.c
@@ -243,12 +243,13 @@ bool br_stp_recalculate_bridge_id(struct
 	return true;
 }
 
-/* called under bridge lock */
+/* Acquires and releases bridge lock */
 void br_stp_set_bridge_priority(struct net_bridge *br, u16 newprio)
 {
 	struct net_bridge_port *p;
 	int wasroot;
 
+	spin_lock_bh(&br->lock);
 	wasroot = br_is_root_bridge(br);
 
 	list_for_each_entry(p, &br->port_list, list) {
@@ -266,6 +267,7 @@ void br_stp_set_bridge_priority(struct n
 	br_port_state_selection(br);
 	if (br_is_root_bridge(br) && !wasroot)
 		br_become_root_bridge(br);
+	spin_unlock_bh(&br->lock);
 }
 
 /* called under bridge lock */


Patches currently in stable-queue which might be from razor@blackwall.org are

queue-4.0/bridge-fix-br_stp_set_bridge_priority-race-conditions.patch
queue-4.0/bridge-fix-multicast-router-rlist-endless-loop.patch